1. Field of the Invention
The present invention relates to a parabola antenna and more particularly to a structure for a parabola antenna for a satellite broadcasting system. It also relates to a method for manufacturing such an antenna.
2. Description of the Prior Art
In conventional parabola antennae, in order to cope with problems of resilient distortion, permanent deformation, damage and the like of parabola surfaces due to the strong wind, there have been effected designs, which are satisfactory in mechanical strength, by increasing the thickness of each of the structural members and providing suitable reinforcements thereto. However, such designs are insufficient to reduce the amount of material required or to save the mounting space to a minimum the greatest possible extent. Thus, there are many problems to be solved for the home use of a parabola antennae in compliance with the recent new application of satellite broadcasting systems.
Referring now to FIGS. 1 and 2, a conventional parabola antenna will be described. FIG. 1 is a partially fragmentary side elevational view of the conventional parabola antenna and FIG. 2 is a rear view of the antenna.
In FIGS. 1 and 2, a parabola surface 1 is mounted on a mounting member 3 through a reinforcement portion 2 and is fixed to a post 4. Electric waves in the air come in the direction indicated by the arrow and are reflected on the parabola surface to be collected by a converter 5. In the antenna shown, the focus of the parabola is offset with respect to the direction of the electric waves, so that shades of the converter 5 and its support 6 are not projected onto the parabola surface 1. Since such an offset type parabola antenna is available for use even in a snowfall, almost all of small size parabola antennae are of the offset type.
The most serious problems in the parabola antennae are the deformation and the damage due to the wind. In order to prevent the accurate parabola surface from being resiliently deformed or from being vibrated at its peripheral portion due to the wind pressure, it is necessary that the outer peripheral portion of the parabola surface 1 be strong enough to resist a force which acts to open the marginal portion of the parabola surface 1. To meet this requirement, a flange 7 is provided along its circumference and the thickness of the parabola surface is also increased.
On the other hand, there is a fear of deformation or damage of the parabola surface 1 due to a bending moment applied to the parabola surface 1 in the vicinity of the mounting portion 2 of the parabola surface. To cope with this, even if the thickness of the parabola surface 1 at the mounting portion 2 of the parabola surface would be rather increased, the mechanical strength thereof would be insufficient. Instead, radial ribs 8 are provided which extend radially outwardly from the mounting portion 2. In such a case, all the moment is applied to the radial ribs 8. Therefore, the effect of the thickness of the central material for the parabola surface 1 is hardly obtained.
As described above, in the conventional antenna, the reinforcements for preventing the deformation of the parabola surface, such as the increased thickness of the marginal portion of the parabola surface and the outer peripheral reinforcement flange 7, and the reinforcements such as the mounting portion 2 resisting against the bending moment applied to the mounting portion due to the wind pressure and the radial ribs 8 for transmitting the moment from the mounting portion, respectively, serve independently of each other. Such a structure as a whole requires a great amount of material.